This vast stretch of Southern Highlands looks at first glance like the biggest unbroken desert left on Mars. At the lower right is red, flat Cimmeria. Aside from craters and ejecta, it's a monotonous dry plain.

But in the center of the photo, everything changes. Promethea is a rugged land downwind of the Hellas Sea, and while it technically qualifies as desert, it's full of snowy mountains with conifer woods in sheltered canyons, short fertile river valleys dead-ending in salt lakes, and deep crater-oases like Kepler (dead center).

To the north, in the upper left, is Hesperia, the land that convinced most scientists that Mars had once been wet--though the Hesperian Age may have been too brief for life to settle the land. Ancient stream channels wrinkle this plateau, which is nearly mountain-and crater-free. Today, while the land is as rusty red as Australia's outback, and streams are still small and intermittent at best, dry grass anchors the dust--it's a dry, windy, often chill prairie, but alive again, after a billion-year sleep--a land of bison, wild horse, and wolf.

Beyond the huge crater-oasis of Herschel (top center) pioneering trees turn the steppe into savanna; slowly the trees thicken until, near the equator, the Great Escarpment drops us (and quite a few waterfalls) into the Aeolian rainforest.